Try a pattern for a cheerleader's skirt (not an all-in-one bodysuit with attached skirt, but a pattern for just the pleated skirt)! You can mark the pattern pieces at 2 lengths, with the first one maybe 2/3 the length of the other; just tape it in place if you don't want to cut it. Pin them together, and sew them as one, to make it two-tier. (Try Simplicity 4060; even though the pattern shows inverted pleats, it's easy to turn them into regular pleats!)

Using a stiffer polyester fabric (i.e., the stuff we used to joke was flammable, in gym class, back in the 80s...!), would be perfect, I would think especially after it was ironed (low-heat, though; you don't want to test that whole "flammable" theory!) *grin*

My teenaged daughter is already planning to go as Vanellope; the light-green hoodie is gonna be restrung with some kind of red, for the "licorice" lacing tie. Cheers to Disney's newest princess!